Gandhi extended her condolences to the families of the bereaved, an official statement said.
"Sonia Gandhi has expressed shock and dismay over the bomb blast," it added.
At least 55 people, including 11 women and three security personnel, were killed and nearly 200 injured when a suicide attacker detonated a powerful bomb at Wagah in Pakistan today, minutes after the popular flag-lowering ceremony at the main Indo-Pak land border crossing.